Ethyl cellulose stabilized with an organic copper salt



Patented July 24, 1951 ETHYL CELLULOSE STABILIZED WITH AN I ORGANIC COPPER SALT Peter Van Wyck, Wilmington, Del., assignor to Hercules Powder Company, Wilmington, Del., a corporation of Delaware No Drawing. Original application June 10, 19.44,.

Serial No. 539,793, now Patent No. 2,445,374,- dated July 20, 1948. Divided and this application May 7, 1948, Serial No. 25,794v

This invention relates to compositions of star:-

'bilized ethyl cellulose which retain their viscosity andgood color after exposure to heat and oxygen. It has been previously recognized that cellulose ethers must be so prepared as to withstand the degradation effects of heat and oxygen. Al-

8 Claims. (Cl. 106194) though various methods of stabilizing cellulose ethers to make them resistant to decomposition have been suggested, such as hydrogenation, treatment with diazomethane, etc, no simple means of stabilization -has proved thoroughly satisfactory.

- Prolonged storage of the flake, and the heat and oxygen present :during molding operations cause embrittlement of the compositions made therefrom. due to viscosity degradation of the ether and, in addition thereto, objectionable color for mation. Previously proposed methods of stabilizing cellulose ethers, such as low pH adjustment of i the flake, sometimes correct one or the other of these defects, but the simultaneous stabilization of both color and viscosity to a satisfactory degree is diflicult,-and usually impossible, to per-" form by previously known procedures. To obtain a satisfactory end product, such as film, lacquer" or molded article, it is necessary to have'fiake stability as well 'as composition stability, since, without the former, the latter is usually impos-' sible. Now, in accordance with this invention, the viscosity stability of cellulose ethers and of their compositions has been greatly improved, while maintaining good color stability, by the additionof a material containing copper in free or com-" bined state, either to the flake or to the ether composition. It has been found that copper and copper compounds exert a definite stabilizing effect on cellulose ethers ;or their compositions, protecting them from degradation when exposed toheat or oxygen. i f

As illustrative of carrying out the invention, the following examples are typical:

EXAMPLE 1 tions of the films before heat-treatment. Table I compares results obtained with original (unstabilized) and stabilized ethyl cellulose.

TABLE I Per Cent P c t ti t er en 0 1scos1 y Stablhzer I On in Film After 16 Hours at No Stabilizen: ..'....l--..'.... 0 -42. Powdered copper....-. 0.0015 93.4 Cupric nitrate... 0.0012 96; 5' Cupric sulfate.-- 0.0010 89. 8 Cupric chloride 0.0015 89. 8 Cuprous chloride. 0.0015 81. 5 Cupric phosphate. 0.0015 51. 3 Cupric carbonate... 0.0010 55. 4 Copper arsenate.... 0.0015 53. 5' Cupric oxide. 0. 0014 87. 3 Copper ammonium chlor 0.0015 90. 7 Copper acetate 0. 0016 87. 6 Copper citrate 0.0015 60. 7 Copper benzoyl benzoate..' 0.0013 89. 0

To 100 grams of granular medium-viscosity ethyl cellulose (44.7% ethoxyl) was added 600 gramsof- %..isopropyl alcohol. To this suspension, 0.025 gram hydratedcupric acetate with that-used iin Example 2, was added 600 grams ofgdistilled' water. {To this suspension, an aqueous solution; containing 0.0375 gram of hydrated cupric acetate was added with stirring.

Agitation; draining, and drying were carried out as in Example 2. Substantially all of the coppercompoundwas absorbed. v I

- EXAMPLE 4 To 400 grams of flake ethylcellulose, identical with that used in Examples 2 and 3, was added 0.15 gram of hydrated cupric acetate which had previously been groundto pass a -mesh sieve.

The copper compound was uniformly-distribute by subsequent tumbling for 15 minutes.

Table II presents a comparison between the un-- treated ethyl cellulose and the stabilized ethyl; cellulose produced-by the methoddescribed-in To 100grams in dry e hyl cellulose, identical To 200 grams of medium-viscosityethyl cell'ulose (44.5% ethoxyl) were added 200* grams of EXAMPLE 9 Ethyl cellulose, identical with that used in Example 8, was treated according to the method described in, U; 8.. Patent No. 1,448,091; To 400 grams of the resulting ash-free product, suspended in 2,000 grams of isopropyl alcohol, was added 0.02 gram cuprammonium hydroxide. Stirring, draining, and drying were carried out as described in Example 2.

Table IV presents a comparison between the ash-free ethyl cellulose and the ethyl celluloses resulting from the treatments described in Examples 8 and 9'.

AsTable-Ishows, a wide variety of copper stabilizers: is available; These include the inorganic salts, such as the sulfates, nitrates, arsenates, chlorides, carbonates, and phosphates; the or- TABLE IV Stability data on Examples 8 and 9 Viscosity Copper Copper Sam 1e O r1gmal: A-fterlt Ash as Added in Analysis p Viscosity Hrs. at NazCOr P; P. P. P. M

160'O E C of E.,C

Per cent I Ash-free ethyl cellulose 94- 3.0 r 1111'- 0 1 (I Ethyl cellulose from Example 8 94. 80.0 0.010 120 E 17; Ethyl cellulose from Example 9 94 60. 0' 0.020 50 37.:

Walter and 850 grams of 41% isopropyl alcohol to: give a final. mixture containing 33% isopropyl, alcohol based on the total weight of the liquid present. The pH of the mixture Was: adjusted to 35.6; with glacial acetic acid, after which 0.024

gram hydrated cupric acetate was added. The sample was. stirred, drained, and. dried. as, de-

scribed in- ExampleZ.

' EXAMPLE 6 Example 5 was repeated, the only change being that a pI-I of 7.1 wasiusedrinstead of the pH used in Example. 5...

f EXAMPLE?? Example 5 was repeated, the only change being that a pH of 8.2-was. used insteadof the pH used in Example 5 Tabl e III presents a comparison between the untreated ethyl cellulose and-theethyl celluloses' prepared according to the methods described in: Examples 5', 6, and- 7.

Medium-viscosity ethyl cellulose (46.5% eth-- oxyl): was treated with dilute acid according to;

the method described in U. 8. Patent No.-

1,448,091. To 400' grams of-ithe-resultingash-free-v product was'added 2 ,000 grams-ref: 35% isopropyl aloohol containing 0.048 gramcupric chloride.

The 'ethyt' cellulosewasstirred; drained, and

dried as described in Example Zabove,

garlic derivatives;. such: as the citrates, acetates. and benzoates; complexes, such as: cuprammonium: hydroxide and; chloride;; ands copper itself, inztheiorm of'copper'or'bronze-dusts;

The stabilizers: are efiective verysmall pro portions, as. shown. by." the tables: and examples-.- From; about; 0.001%; to: 0;005,%, is; a. convenient: rangeof copper: concentration. which gives: efieetitle; stabilization; in general, a quantitybetweem about 0;000 5%, and: 0.03% is, preferred; When relatively. inactive. substances;vv such as copper: naphthenate orxcopper-cxalate, areused', asimuchfi asabout. 1,% I mayrbenecessarmbut. with theemost' active agents, suclrastcoppen nitrate (seev Table: V), as little as; about 0.0002% gives; satisfactory: stabilization. In. general; for all stabilizers, a suflicient: quantity to stabilize. the ether, within: the range between. 0.0002:% and 1 the.=pe1i'-'- centage being that of copper on the basis ofxthe celluloseet-her: stabilized; is utilized; Copper, in the form: of; copper nitrate, was incorporated in filmsin the quantities shown, after; which. the:- films were; heat-treated. in. the manner: herein?! after described,

TABLE". V

. RPt'zergentf Per Cent 8 an 9 VlSCOSlty' Cum F1111 AfterlfilHours' 0. 42.7. 0. 00013 46. 5'- 0.00026 78.3 0. 00039. sec 0.00078 87:0

accuses 'rWhile ethyl cellulose is'usedin the examples to illustrate the invention, thesestabilization treatv mentsapply equally well to cellulose ethers generally, for example, other alkyl cellulose ethers suchas methyl cellulose and propyl cellulose; aralkyl ethers such asbenzyl' celluloseymixed ethers 'such as methyl-ethyl, methyl-benzyl, or ethyI-benzyl celluloses; carboxy ethers such as sodium carboxymethylcellulose. .Water-sol uble ethers and organic solvent-soluble types of ethers are included.' All cellulose ethers are subject to the degradation processes herein de-* scribed which occur when said ethers are sub.-. jected to heating and oxidation. The addition of copper or copper compounds to such ethersor their compositions constitutes an effective means for minimizing or changing the degradation mechanisms. v 1 The degree-of substitution and'viscosity of the cellulose ethers do not affect the stabilizing action ofthe added copper or copper compounds. When ethyl cellulose is used, the commercially available types usually contain between about 44.5% and 50% ethoxyl. For molded articles, a'viscosity of about 100 centipoises is usually used, and films are frequently made up of 50-centipoise viscosity grade. Lower viscosity grades are usually used'in lacquers,- varnishes, etc., principally material of about 22 centipoises or less. All are effectively stabilized in accordance with this in-' vention. Y

Plasticizers for cellulose ethers, such as tributylphosphate, tricresylphosphate, triphenylphosphate, dimethyl phthalate, diethyl phthalate, dibutyl phthalate, diamyl phthalate; diphenyl phthalate; vegetable oil fatty acids, such as castor oil fatty acids; fatty alcohols, such as lauryl alcohol; vegetable .oils and mineral oil, linseed oil, etc. may be incorporated in an amount necessary to the particular use to which the composition is to be put. In addition, there may be mixed with the cellulose ethers various compatible resins, such as wood rosin, hydrogenated rosin, gum C ongo', dammar, cumar, phenolics, modified phenolics, alkyds, ester gum, shellac, etc., as well 'as filler pigments, and coloring matter. Swelling agents, such as methyl alcohol, ethyl alcohol, and mixed solvents, such as ethyl alcohol and acetone, maybe used instead of the isopropyl alcohol shown in Example 2.

The amount of swelling agent used in the steeping bath is subject to wide variation, dependent upon the specific swelling agents, the steeping time, and the temperature employed. Concentrations between about 15% and 40% of the swelling agent have been found suitable. However, use of a swelling agent is not essential.

The temperature of the steeping treatment may vary between about C. and about 100 C., but the range between about 15 C. and about 70 C. is preferred. The time of steeping may be from about minutes to several hours, but about 30 to 60 minutes is a preferred period. If no swelling agent is used, as in Example 3, the steeping time is usually between about 1 to 3 hours.

As shown by Example 4, an effective way of adding powdered copper compounds is by incorporation with the dry grains, involving a simple tumbling operation to effect distribution. Although the use of copper acetate is shown by Example 4, bronze dust, copper dust, or finely-divided copper compounds other than the acetate may be added in the same manner. Another useful method of copper stabilization is the addition of copper or-copper compoundsduring molding powder formation orin lacquer formation.

The stability tests carried out on samples shown in'Tables I and V involved theheating of films-at -C. for 16 hours. The remaining samples were tested by: the following method: Films 0.1 to 0.15 millimeter in thickness were prepared by spreading",io n' glass plates,1'2.5% solutions of the ethylcellulose dissolved in 70-30 toluene-alcohol.- The film was dried in air for 3 hours and in an oven'zat 70 C. for 2: hours. Sections of the film 6 by 3inches were then cut and pleated by folding in accordion shape and placed in thebottom of a lO-inch test tube which was left open at the top. The 'testtube with the inserted film was placed in a forced draft oven adjusted to C. L-1.C. and heated for 1 /2 hours. The film was then removed, immediately placed in a stoppered bottle, weighed after cooling, and made up to a 5% solution in 80-20-toluene-alcohol. The viscosity of the heat-degraded film solution was then measured at 25 C. and compared with the viscosityof another portion of the same film which'ha not been'given the heat-treatment. I

As shown by Table I, copper stabilization is effective regardless ofthe anionic component which has been added. However, as shown by Table III,

the pH at which copper treatment is carried out usually predetermines the extent to which the copper compound is absorbed by the cellulose ether. While thistable shows that the absorption of copper'occurs over a wide pH range, the higher pHs cause greater copper absorption and, hence, are to be preferred.

The majority oftreatments to which cellulose ethers are normally subjected for ash removal or viscosity degradation cause viscosity instability of the resultant product. However, as shown by Examples 8 and 9, this adverse acidic condition is counteracted by the addition of copper to the unstable material. The advantages of the use of copper and copper compounds as stabilizers for celluloseethers reside in the following The copper and copper compounds are easily incorporated with the ethers at any stage of the aftertreatment or during lacquer or plastic formation; unlike numerous other stabilizers, viscosity is effectively protected against degradation by heat or oxygen without the concurrent formation of objectionable colored decomposition products; the extent of stabilization is excellent and superior to that obtained with most other stabilizers; and only extremely minute quantities of the stabilizer are ordinarily needed.

Thus, according to the present invention, copper-containing materials have been found to be very effective heat stabilizers for cellulose ethers and their compositions, with or without plasticizers and other ingredients. The terms coppercontaining materials and materials containing copper are meant to include copper per se, bronzes and brasses, inorganic compounds and organic copper compounds. All concentrations discussed or claimed will be understood to mean percentage of copper in the cellulose ether, not

percentage of copper-containing material in the ether.

This application is a division of my application, Serial No. 539,793, filed June 10, 1944, now Patent No. 2,445,371, issued July 20, 1948.

What I claim and desire to protect by Letters- Patent is:

1. As a new composition of matter, an ethyl cellulose characterized by the presence therein of 7115. an agent capable of 'stabilizing the ether against the degrading efi'eets' 'ofheat andoxygen without reducing the viscosity ofthe ether; said: agent being anorganie sa'lt of copper of the g'roup'con sitting of copper acetate, copper citrate, copper. benzovl' benzoate," copper naphthenate, amtcope per oxalate in a sufficient amount to stabilize the other within the range-from about: 0.0002%@ to: about 1 of copper based on the weight of the: ether.

As a new: composition o'f'matten. aneethy]: cellulose characterized bythe presence thereimof an: agent capable of stabilizing the ether; against the degrading effects of heat and oxygenwithout reducing the viscosity of "the ether, said agent tie-- in'g copper. acetate; ina suflicient, amount: to stabilize theether within the i range fromqabout 0.00U2%" to' about l;%'-"0f' copper! based. on the weight of the-eth'er.

3. As a new composition of'matter; an-etliyll cellulose characterized by; the: pres'enceztherein- 013 an agent capable of'stabilizin' the: ether-against. the degradingeffects of? heat: and" oxygen withr out reducing theaviscosity of; the ether; said; agent: being copper citrate-v in ajsufl'lcient amount, to stabilize the other within: the rangefrom about 010002176 to about: 1% of copper'basedaon: the weight ofthe ether;

As anew composition of matter; arr; ethyl: cellulose characterized" by the presencetherein of an agent capable of stabilizing the ether;

against the degrading effects-ofheat andoxygen;

without reducing theviscosity; of the-ether, saint agent being copper benzoylibenzoate in -a sufliscientamount" to stabilize: the ether; withimthe range from abut 0.0'002% -'to. ab011t'1% of: copper based-'onthe weight'of: thezethen. 1

i 5; An' ethyl, cellulose plastic composition chan acterizelt by the presence thereingof an agent. oat pable of stabilizing the: composition; against the; degrading efiects of heat withoutv reducing; theviscosity of the composition; saidi agentibeingan organic salt of copperof the group consistingofcopper acetate; copper citratercopperrbenZoylE benzoate, copper naphthenata? and: copper.

III

8. oxalate presentin asuificientamount: to stabilize theetherwithin the range from about: 0.002%;tci about-1%: of? copper basedon the weight?- oi the e her; 2

6: As:v a new: composition. of: mattem. granular. ethyl cellulose: characterized by the presence therein of an agent capable of stabilizing: the ethyl cellulose against the degrading effects of; heat and oxygen withoutreducing the viscosity of the ether; said agent being an organic salt of! copperof the; group consisting" on copper acetate-g. copper citrate, copper; benzoyl; benzoate, coppen naphthenate; and: copper; oxalate in a: suificient amount: to; stabilize; the ether within: the range from about (L0002;% to: aboutil of coppenbased; onzthe weightloftheether;

'7. As a. new composition of matter; anyethyli cellulose characterized by the presence-therein: off an agentJcapable: of; stabilizing the ether against the? degrading effects: of heat. and; Oxygen without reducing the viscosityz oi the ether said agent being copper naphthenate an; amount about: 11% of copper. based: on the weight; of the ether. s

8-. As, a new: composition, of matter, an ethyl= cellulose= characterized, by the; presence therein of: an agent: capable of stabilizing the: other, against the degrading; effects. of heat and oxygen without reducing; the, viscosity ofthe ethensaidi agent being: copper oxalatee im an, amount, about 1% of copper based on the weight of the other.

PETER VAN" WYCK'. V

REFERENCES CITED The following references are of record in the file of this" patent:

UNITED STATES PATENTS Van Wyck Ju1y,20,' 1943" Certificate of Correction Patent No, 2,561,893 July 24, 1951 PETER VAN WYGK It is hereby certified that error appears in the printed specification of the above numbered patent requirmg correctlon as follows:

Column 6, line 71, for the patent number 2,445,37 1 read 2,445,374;

and that the said Letters Patent should be read as corrected above, so that the same may conform to the record of the case in the Patent Ofiice.

Signed and sealed this 2nd day of October, A. D. 1951.

THOMAS F. MURPHY,

Assistant Commissioner of Patents. 

1. AS A NEW COMPOSITION OF MATTER, AN ETHYL CELLULOSE CHARACTERIZED BY THE PRESENCE THEREIN OF AN AGENT CAPABLE OF STABILIZING THE ETHER AGAINST THE DEGRADING EFFECTS OF HEAT AND OXYGEN WITHOUT REDUCING THE VISCOSITY OF THE ETHER, SAID AGENT BEING AN ORGANIC SALT OF COPPER OF THE GROUP CONSISTING OF COPPER ACETATE, COPPER CITRATE, COPPER BENOZYL BENZOATE, COPPER NAPHTHENATE, AND COPPER OXALATE IN A SUFFICIENT AMOUNT TO STABILIZE THE ETHER WITHIN THE RANGE FROM ABOUT 0.0002% TO ABOUT 1% OF COPPER BASED ON THE WEIGHT OF THE ETHER. 